1. Field
This patent specification relates to a method and apparatus for image forming, and more particularly to a method and apparatus for image forming that is capable of effectively performing an image fixing process using a sheet-like-shaped member for forming a heat and pressure nip.
2. Discussion of the Background
FIG. 1 illustrates a typical structure of a background fixing apparatus that is employed in an electrophotographic image forming apparatus to fix a toner image on a recording sheet. As shown in FIG. 1, the background fixing apparatus includes a heat fixing roller 1 which is provided with a heater 2 arranged inside for heating and a pressure fixing roller 3 arranged in pressure contact with the heat fixing roller 1. The fixing apparatus further includes a temperature detector 4 for detecting a surface temperature of the heat fixing roller 1 heated by the heater 2, a guide plate 5 for guiding a recording sheet into an area between the heat fixing roller 1 and the pressure fixing roller 3, a separation pawl 6 for separating the recording sheet wrapping around the heat fixing roller 1 from the heat fixing roller 1, and a pair of transfer rollers 7 arranged in a sheet exit side of the fixing apparatus.
Into this fixing apparatus, a recording sheet having a toner image thereon is transferred and is guided by the guide plate 5 to a nip area formed between the heat fixing roller 1 and the pressure fixing roller 3. The toner image on the recording sheet is subjected to heat and pressure in the nip area and is fixed on the recording sheet. After that, the recording sheet having the fixed toner image thereon is transferred and is ejected outside the fixing apparatus with the pair of transfer rollers 7. As the recording sheet passes through the nip area, toner particles attached to heat fixing roller 1 are removed by a cleaning pad (not shown).
The surface temperature of the heat fixing roller 1 is detected by the temperature detector 4 and, based on the detection result by the temperature detector 4, a heat controller (not shown) controls the heating of the surface temperature of the heat fixing roller 1 with the heater 2.
Conventionally, the background fixing apparatus employing a pair of the above-described heat fixing roller 1 and the pressure fixing roller 3 generally adopts an infrared heater or a halogen heater as a heating element. However, the pressure fixing roller 3 has a relatively large heat capacity due to its structure that typically uses a core metal covered with a silicone rubber layer on which a release layer made of polytetrafluoroetylene (e.g., TEFLON) is formed. Because of this large heat capacity, the pressure fixing roller 3 takes a relatively long time to heat, after the heating of the heat fixing roller 1 with the heater 2 is started. This tendency grows with a control developed in recent years with consideration given to energy savings and becomes a major factor causing a failure of the fixing process. Further, this background fixing apparatus has another drawback that the components involved are relatively expensive.
In addition, the background fixing apparatus presses the heater fixing roller 1 against the pressure fixing roller 3 with a relatively large force in order to maintain a predetermined width of the nip area, and such large force produces a stress relative to the recording sheet transferred by the heater fixing roller 1 and the pressure fixing roller 3. As a result, the recording sheet may form wrinkles therein. These wrinkles are referred to as a fixing wrinkles.
To attempt to avoid the fixing wrinkles, a fixing apparatus is developed which employs a pressure member having a sheet-like shape in place of the pressure fixing roller 3 and contacts such pressure member with the heat fixing roller 1 so as to form a nip area between the pressure member and the heat fixing roller 1. In this configuration, the pressure member is prone to be quickly heated due to the sheet-like shape thereof. Also, the nip area is given a predetermined width without causing fixing wrinkles in the recording sheet.
However, the above-mentioned fixing apparatus using the pressure member in the sheet-like shape has a drawback that the nip width is varied and accordingly types of available recording sheets may be limited. That is, in order to arrange the pressure member to press the heat fixing roller, a spring or the like may be disposed at a position opposite to the heat fixing roller relative to the pressure member to press the pressure member against the heat fixing roller. Under such a circumstance, the pressure member may be moved slightly in accordance with the thickness of the recording sheet and, as a result, the nip width may be varied.
This patent specification describes a novel image fixing apparatus that uses a sheet-like-shaped member. In one example, a novel image fixing apparatus includes a fixing roller, a sheet-like-shaped member, a sheet supporter, and a stopper. The fixing roller includes a heater and is configured to rotate to forward a recording sheet having a toner image. The sheet-like-shaped member is configured to contact the fixing roller to form a nip area with the fixing roller. The sheet supporter is configured to support the sheet-like-shaped member at an upstream side of a bottom surface of the sheet-like-shaped member in a direction in which the recording sheet is transferred. The stopper is configured to stop a free side of the sheet-like-shaped member so that the free side of the sheet-like-shaped member is not lowered from a predetermined position.
The stopper may be configured to be movable, and the image fixing apparatus may further include an adjustment mechanism which is configured to move the stopper to adjust a vertical position of the sheet-like-shaped member.
The stopper may be configured to be an eccentric roller having an eccentric shaft and the adjustment mechanism including a shaft supporter for supporting the eccentric shaft and an adjuster for turning the eccentric shaft.
The eccentric shaft may be configured to have a cross section of a polygonal and the shaft supporter may be configured to have a V-like-shaped portion to be engaged with a corner of the polygon of the eccentric shaft.
The adjuster may be connected to the eccentric shaft and may be configured to have indexes for indicating information associated with turning positions of the eccentric shaft corresponding to vertical positions of the sheet-like-shaped member.
The information indicated by the indexes may include applicable thickness of a recording sheet corresponding to the vertical positions of the sheet-like-shaped member.
The novel image fixing apparatus may further include a moving mechanism configured to move the fixing roller to make contact with the sheet-like-shaped member.
The moving mechanism may include a holding member configured to hold the fixing roller for rotation and a pressing member configured to apply a force to the holding member in a direction toward the sheet-like-shaped member.
The holding member may be provided with a turning shaft at a position different from a rotation axis of the fixing roller so that the holding member is caused to pivot about the turning shaft by the force of the pressing member to make contact with the sheet-like-shaped member.
The moving mechanism may further include an actuating lever configured to switch to a first position to hold the holding member against the force of the pressing member such that the fixing roller is separated from the sheet-like-shaped member and to a second position to release the holding member so that the fixing roller is made in contact with the sheet-like-shaped member, and a stopper provided to the holding member for stopping the actuating lever at the first position.
The sheet-like-shaped member may be made of a rigid and heat-resistant resin.
This patent specification further describes another novel image fixing apparatus. In one example, this novel fixing apparatus includes a plurality of rollers, a sheet-like-shaped member, a holder, and a stopper. The plurality of rollers includes at least one fixing roller containing a heating source. The sheet-like-shaped member contacts the fixing roller, forms a nip area therewith, and is made of a rigid and heat-resistant resin. The holder is configured to hold one side of the sheet-like-shaped member. The stopper is configured to stop a free side of the sheet-like-shaped member such that the free side of the sheet-like-shaped member is not lowered below a predetermined position.
This patent specification further describes a novel method of image forming. In one example, the novel method includes the steps of providing, arranging, supporting, applying, stopping, and transferring. The providing step provides a fixing roller that includes a heater and is rotated to be able to forward a recording sheet having a toner image in a sheet transfer direction. The arranging step arranges a sheet-like-shaped member made of a rigid and heat-resistant material under the fixing roller. The supporting step supports the sheet-like-shaped member at an upstream side of a bottom surface of the sheet-like-shaped member in the sheet transfer direction. The applying step applies a pressure to the fixing roller so that the fixing roller is made to contact under pressure with the sheet-like-shaped member so as to form a nip area therebetween. The stopping step stops a free side of the sheet-like-shaped member so that the free side of the sheet-like-shaped member is not lowered from a predetermined position. The transferring step transfers a recording sheet having a toner image thereon into the nip area in the sheet transfer direction.
This patent specification further describes a novel image forming apparatus. In one example, the novel image forming apparatus includes an image fixing apparatus including a fixing roller, a sheet-like-shaped member, a sheet supporter, and a stopper. The fixing roller includes a heater and is configured to rotate to forward a recording sheet having a toner image. The sheet-like-shaped member is configured to contact the fixing roller to form a nip area with the fixing roller. The sheet supporter is configured to support the sheet-like-shaped member at an upstream side of a bottom surface of the sheet-like-shaped member in a direction in which the recording sheet is transferred. The stopper is configured to stop a free side of the sheet-like-shaped member so that the free side of the sheet-like-shaped member is not lowered from a predetermined position.